The invention relates to a screw compressor for compressing a working medium, comprising an outer housing, two screw rotors which are arranged in the outer housing in rotor bores provided for them and a drive for the screw rotors.
In the case of screw compressors of this type, the sealing gap formed between the screw rotors and the rotor bores is a critical parameter since this is responsible for the leakage. The sealing gap normally varies on account of thermal or other influences.
The object underlying the invention is therefore to improve a screw compressor of the generic type in such a manner that the sealing gap is subject to as little variation as possible.
This object is accomplished in accordance with the invention, in a screw compressor of the type described at the outset, in that a compressor screw housing, in which the rotor bores for the screw rotors are arranged, is provided within the outer housing and that a space is arranged between a substantial part of the compressor screw housing and the outer housing.
The provision of a space serves in this respect to couple the compressor screw housing and the outer housing as little as possible thermally and with a view to vibrations or even decouple them. The effects on the compressor screw housing of external, thermal influences acting on the outer housing of the screw compressor are thus reduced and the compressor screw housing itself has the possibility of taking up a thermal state of equilibrium and of remaining in this state, at least only with long-term variations. Moreover, vibrations of the compressor screw housing are transferred to the outer housing to a lesser extent.
With respect to the design of the compressor screw housing, no further details have been given in conjunction with the preceding embodiments. One advantageous embodiment, for example, provides for the compressor screw housing to have an inlet section, a compression section and an outlet section.
With respect to the extension of the space in azimuthal direction to the rotor bores, it is particularly advantageous when the space extends over at least half the circumference of the compression section in azimuthal direction.
It is particularly favorable when the space extends over at least approximately three quarters of the circumference of the compression section in order to thus disconnect as large a portion of the compression section as possible from the outer housing thermally and with regard to vibrations.
With respect to the extension of the space in the area of the inlet section of the compressor screw housing, no further details have so far been given. It is, for example, particularly favorable when the space extends in azimuthal direction to the rotor bores over at least half the inlet section. It is even better when the space extends over three quarters of the circumference of the inlet section in azimuthal direction.
Furthermore, no further details have been given in conjunction with the preceding explanations concerning individual embodiments with respect to the extension of the space in the area of the outlet section. Since the outlet section is in any case, on account of the exiting working medium, at the temperature thereof, it is in principle not absolutely necessary for the space to extend in the area of the outlet section, as well.
However, it is likewise advantageous when the space also extends in circumferential direction over the outlet section in order to bring about an even more uniform temperature in this section.
It is likewise particularly advantageous when the space extends over at least half the circumference of the outlet section in azimuthal direction, even better over approximately three quarters of the circumference of the outlet section in azimuthal direction.
With respect to the extension of the space in axial direction of the screw rotors, no further details have likewise been given in conjunction with the preceding explanations concerning the individual embodiments. One advantageous embodiment, for example, provides for the space to extend on average over at least half of a length of the compressor screw housing extending in axial direction of the screw rotors.
In this respect, it is expedient when the space extends from an end of the compressor screw housing on the outlet side in the direction of an end thereof on the inlet side.
In this respect, it is especially favorable when the space extends at least over the compression section in axial direction.
It is particularly favorable when the space extends as far as the inlet section and thus already contributes to a decoupling of the compressor screw housing and the outer housing in the area of the inlet section.
In conjunction with the inventive solution, it has merely been assumed so far that the space serves to bring about a thermal and vibrational decoupling between the outer housing and the compressor screw housing.
A particularly favorable utilization of the fact that such a space is present is, however, given when the space is acted upon by pressure so that not only is the compressor screw housing acted upon by the pressure resulting internally in the area of the screw rotors during the compression of the working medium but also, on the other hand, a pressure acting from outside on the compressor screw housing counteracts this pressure. It is particularly expedient when the space is subject to a pressure which corresponds approximately to the end pressure of the screw compressor since, in this case, the compressor screw housing is already acted upon from outside by a pressure which always corresponds to the maximum pressure in the interior thereof during the compression of the working medium and so, in the long run, the compressor screw housing is not subject to any one-sided pressure acting on it but, on average, is acted upon with a pressure which is greater than the pressure resulting in the interior thereof.
This solution has the particular advantage that the compressor screw housing need be dimensioned with respect to its mechanical stability only such that it keeps the sealing gap between the screw rotors and the compressor screw housing essentially constant when pressure acts on it from outside and need not be dimensioned, as in the known solutions, such that it is rigid against deformation in relation to a difference in pressure between the interior pressure which ensues and the surrounding pressure.
With respect to the effect of the space, it has so far merely been assumed that the space effects per se a thermal decoupling between the outer housing and the compressor screw housing. It is particularly favorable, however, especially to reduce any thermal distortion between the inlet section and the outlet section or even avoid such distortion which is caused by the inlet section being at the temperature of the working medium entering it whereas the outlet section is heated by the working medium exiting from it and heated due to the compression, when the compressor screw housing can be temperature controlled.
Such a temperature control may preferably be brought about in that the compressor screw housing can be temperature controlled by a temperature control medium provided in the space.
In principle, it would be conceivable to provide any suitable medium as temperature control medium. For example, it would be conceivable to introduce a special temperature control medium into the space for this purpose. The inventive solution is, however, particularly simple when the temperature control medium comprises the working medium.
A supplementary or alternative solution provides for the temperature control medium to comprise oil from a lubricating oil circuit of the screw compressor since this oil from the lubricating oil circuit is likewise heated to a higher temperature, preferably to a temperature close to the temperature of the compressed working medium.
Such a temperature control of the compressor screw housing by a temperature control medium provided in the space can be brought about either by a standing temperature control medium arranged in the space or by the fact that the temperature control medium flows through the space. For example, this may be realized by the fact that with a working medium serving as temperature control medium the compressed working medium flows into the space and as a result leads to the compressor screw housing being heated up.
An alternative solution provides for the oil serving as temperature control medium to form, in the space, an oil bath which can thus likewise serve to control the temperature of the compressor screw housing and keep it at a temperature which is as essentially constant as possible.
In principle, it would be conceivable to design the compressor screw housing as a part which is detachably insertable into the outer housing. A particularly favorable solution does, however, provide for a section of the outer housing and the compressor screw housing to form an integral part so that the compressor screw housing can be fixed relative to the outer housing in a particularly simple manner and, in addition, a particularly precise, immovable arrangement thereof relative to one another results.
In this respect, it is particularly favorable when the compressor screw housing can be machined by fixing it on the outer housing so that the fixing in place of the outer housing does not have any effect on the shape of the compressor screw housing during machining and thus the fixing in place of the outer housing also does not have any disadvantageous effects on the machining of the compressor screw housing.
An additional, advantageous solution provides for the compressor screw housing to be arranged so as to adjoin a first bearing housing for rotary bearings of the screw rotors, wherein the bearing housing is likewise preferably connected in one piece to the outer housing and to the compressor screw housing.
It is, in particular, favorable when the first bearing housing serves to mount the screw rotors at an end thereof on the inlet side.
In addition, it is provided in an advantageous embodiment of the inventive solution for a second bearing housing arranged so as to be located opposite the first bearing housing to adjoin the compressor screw housing, this second bearing housing serving to mount the screw rotors at an end thereof on the outlet side.
In order to provide for a machining of the compressor screw housing in a simple manner, it is favorable when the second bearing housing is detachably connected to the compressor screw housing.
With respect to the assembly and producibility of the compressor screw housing securely connected to a section of the outer housing, it is preferably provided for the compressor screw housing to extend as far as a flange on the outlet side which is located in axial direction approximately in the area of a connecting flange of the section of the outer housing supporting the compressor screw housing so that the interior of the corresponding section of the outer housing is also accessible for machining from the side of the connecting flange and, in particular, the flange of the compressor screw housing on the outlet side, as well, wherein the flange of the compressor screw housing on the outlet side serves to provide a connection to the second bearing housing.
The compressor screw housing has so far been defined only to the extent that it has two rotor bores for the screw rotors of the screw compressor. A particularly preferred variation provides for a regulatable screw compressor so that the compressor screw housing has, in addition, a receiving means for a regulating slide for regulating the performance of the screw compressor.
In conjunction with the preceding explanations concerning the invention, these have merely concentrated on what effect the space has in the sense of a thermal decoupling and, where applicable, also a temperature control of the compressor screw housing.
Alternatively thereto or in addition thereto, one idea representing its own invention provides for an oil separator path to be provided within the outer housing of the screw compressor for the separation of oil out of the working medium exiting from the compressor screw housing on the pressure side.
The advantage of such an oil separator path which is as great as possible creates the possibility of bringing about an optimum separation of oil out of the compressed working medium. In this respect, the oil separator path is preferably designed such that it reaches from one end of the outer housing located opposite an inlet connection of the outer housing as far as an outlet connection for the working medium located in the area of the compressor screw housing so that the oil separator path has as great an extension as possible.
In order to bring about an optimum oil separation, it is preferably provided for a demister to be arranged in the oil separator path for forming oil droplets from an oil mist in the working medium.
In order to bring about an oil separation and a collection of the oil in a suitable manner, it is preferably provided for an oil sump to be formed in the course of the oil separator path.
The oil separator path could be defined within the outer housing by means of special housing elements. However, a particularly favorable solution provides for the outer housing to guide the working medium while it is flowing through the oil separator path and thus create the possibility at the same time of obtaining as long an oil separator path as possible with as large a cross section as possible, namely the maximum cross section possible within the outer housing which results in the flow velocity of the compressed working medium being very slow and thus of an optimum separation of the oil droplets being possible via the oil separator path.
In this respect, it is preferably provided for the working medium to flow around the second bearing housing in the course of the oil separator path and thus already control the temperature of it. A particularly favorable solution which ensures as long an oil separator path as possible provides for the working medium to flow around the compression section of the compression screw housing, i.e. also flow into the space and thus, on the one hand, effect a temperature control of the compressor screw housing and, on the other hand, the possibility is given of designing the oil separator path with as large a volume as possible and as long as possible.
In this respect, it is particularly favorable when the working medium flows as far as the inlet section of the compressor screw housing in the course of the oil separator path so that the maximum possible length of the oil separator path can be achieved and, on the other hand, an optimum temperature control of the compressor screw housing as far as the inlet section.
Additional features and advantages of the invention are the subject matter of the following description as well as the drawings illustrating several embodiments.